Cast flapper with hot isostatic pressing treatment

ABSTRACT

Components of a subsurface safety valve are cast instead of machined for dramatic cost savings. In particular, the flapper is cast from a 718 nickel alloy and treated with the HIP process to increase strength and corrosion resistance while reducing porosity. Other downhole valve components are contemplated to be produced by the same technique and the materials can also be varied. Depending on the specific alloys, the resulting HIP components are either superior in performance (e.g. strength, corrosion resistance) or considerably cheaper to manufacture than their wrought counterparts.

PRIORITY INFORMATION

This application claims the benefit of U.S. Provisional Application Ser. No. 60/582,614, filed on Jun. 24, 2004.

FIELD OF THE INVENTION

The field of the invention is components for downhole tools that can be cast instead of machined from bar and more particularly subsurface safety valve components that are cast and treated by hot isostatic pressing (HIP).

The HIP process is well known. Hot Isostatic Pressing (HIP), the simultaneous application of heat and high pressure, has become a standard production process in many industries. In the HIP unit a high temperature furnace is enclosed in a pressure vessel. Work pieces are heated and an inert gas, generally argon, applies uniform pressure. The temperature, pressure and process time are all controlled to achieve the optimum material properties.

The Economics of HIPping

HIP processing incorporated as an integral part of the manufacturing process reduces scrap.

HIP frequently allows replacement of wrought components by castings. This reduces the amount of expensive nickel alloy used per part since the casting is near net shape.

HIP castings reduce the machining time compared to starting with bar stock.

HIP can reduce quality assurance requirements by improving material properties and reducing property scatter. In some cases, the savings on radiographic costs will cover the costs of HIP.

Castings

HIP is widely used in the casting industry to remove the internal porosity generated during the casting process. This results in improved strength, ductility and fatigue life of the casting. The rejection rate is reduced and the mechanical properties of the parts are more consistent. Casting alloys that are routinely HIPped include nickel, cobalt, aluminum and titanium.

Powder Metallurgy

HIP consolidates fine powders into components approaching 100% theoretical density. Pre-sintered components are fully densified or powders are encapsulated in a sealed container, then HIPped directly into a near-net shape. The process lends itself to the processing of tool steels, cemented tungsten carbide, copper, nickel and cobalt alloys. Ceramics and composite materials can also be formed in this manner.

Other Applications

HIP is used for the bonding of dissimilar material, consolidation of plasma coatings, improvement of welds, processing soft and hard magnetic material and a variety of ceramic applications. In applications such as turbine engine rebuilding, HIP removes the effects of fatigue in components, which are near the end of their service life. The components can be rejuvenated for further service.

In the oil and gas industry, drill bit components have been HIPped to create hardfacing as illustrated in U.S. Pat. Nos. 6,138,779; 5,758,733 and 5,560,440. The HIP process has been applied to cast nickel alloys requiring high strength and high temperature resistance such as in the aircraft gas turbine industry as illustrated in U.S. Pat. No. 6,632,299. The HIP process has been shown to reduce porosity in titanium castings, as indicated in U.S. Pat. No. 6,705,385. HIPping has been shown to raise the corrosion resistance of aluminum alloys as indicated in U.S. Pat. No. 6,733,726. In the oil and gas industry Camco now a part of Schlumberger made castings of a nickel alloy S-monel for a few downhole tool components but discontinued the practice because the resulting components were not acceptable to meet an industry standard for hydrogen sulfide service. That standard MR0175 was put out by the National Association of Corrosion Engineers (NACE) and has been adopted by many state and national regulatory agencies and many well operators.

Cast parts often can result in substantial cost savings over wrought parts despite the need for some finish machining on the cast parts. Savings of approximately 70% of the cost of a fabricated part are possible. In the area of subsurface safety valves, flappers and their mating seats involve intricate machining and present an opportunity for cost savings using HIPping. Despite the existence of the HIP process for over 30 years and the use of subsurface safety valves throughout that period, no manufacturer has combined the HIP technology to treat parts for downhole safety valves as is contemplated by the present invention. In fact, those skilled in the art have tried casting parts that used to be fabricated, to save production cost, but have given up in the face of the compromises required when casting the parts particularly in the areas of strength, porosity, fracture toughness and diminished corrosion resistance. The present invention recognizes that the savings from casting components for downhole tools can be captured by using HIPping. More particularly, the savings can be achieved for cast nickel alloys and more particularly when the components are a flapper and associated parts of a subsurface safety valve. These and other aspects of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below.

SUMMARY OF THE INVENTION

Components of a subsurface safety valve are cast instead of machined for dramatic cost-savings. In particular, the flapper is cast from a 718 nickel alloy and treated with the HIP process to increase strength and corrosion resistance while reducing porosity. Other downhole valve components are contemplated to be produced by the same technique and the materials can also be varied. Depending on the specific alloys, the resulting HIP components are either superior in performance (e.g. strength, corrosion resistance) or considerably cheaper to manufacture than their wrought counterparts.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a section view of a subsurface safety valve, shown in the closed position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a subsurface safety valve, SSV, in the closed position. A flapper 10 is pivoted closed by a coiled spring 12 against a seat 14 when the flow tube 16 is raised by closure spring 18 upon failure of pressure at control line connection 20. FIG. 1 illustrates a known SSV. The invention lies in the manner of producing the components, particularly the flapper 10 and its associated seat 22. The preferred material is a nickel 718 alloy and it is preferably cast and HIPped and then subjected to finish machining to get the component to its dimensional tolerances. The HIPping reduces porosity and increases strength and improves corrosion resistance. While the flapper can be produced by this technique with a resultant cost savings of nearly 70% over machining the part from bar stock, it will be understood that other components of the SSV such as the seat 22 or the flow tube 16 or other parts can be made from the same casting and HIPping technique. While the preferred material for the flapper 10 is a nickel 718 alloy, other materials can be cast and Hipped for downhole tool components to achieve the cost savings and performance improvements reported above.

Those skilled in the art know that although SSVs have been available for many years, their components have been machined from bar stock at much higher cost than casting and finish machining. On one known occasion where casting parts for downhole tools was used in an SSV, the parts were not HIPped and their suitability particularly in hydrogen sulfide service was limited. Those skilled in the art tried and failed before to produce components for SSVs that had the necessary strength, corrosion resistance and porosity levels to meet a variety of operating conditions downhole. This is the case despite the availability of the HIP process for over 30 years.

While the invention focuses on casting a nickel 718 allow for flappers in SSVs, those skilled in the art will appreciate that other materials may be cast and HIPped for use in downhole tools as a component. The range of components is not limited to SSVs in the area of downhole tools. Different materials can be used for discrete components in a given tool and be cast and HIPped to achieve the aforesaid advantages.

While the preferred embodiment has been set forth above, those skilled in art will appreciate that the scope of the invention is significantly broader and as outlined in the claims which appear below. 

1. A method of manufacturing components for a downhole tool, comprising: casting the component; subjecting the component to a HIP process; finish machining said component to a desired dimension.
 2. The method of claim 1, comprising: producing engaging components of the downhole tool.
 3. The method of claim 1, comprising: producing a flapper for a safety valve.
 4. The method of claim 1, comprising: producing a seat for a flapper in a safety valve.
 5. The method of claim 1, comprising: producing a flow tube for a safety valve.
 6. The method of claim 1, comprising: using a nickel alloy for the material for said casting.
 7. The method of claim 1, comprising: using 718 nickel alloy for the material for said casting.
 8. The method of claim 1, comprising: reducing porosity of said casting with said HIP process.
 9. The method of claim 1, comprising: improving corrosion resistance of said casting by said HIP process.
 10. The method of claim 1, comprising: increasing strength of said casting by said HIP process.
 11. The method of claim 3, comprising: using a nickel alloy for the material for said casting.
 12. The method of claim 10, comprising: using 718 nickel alloy for the material for said casting.
 13. The method of claim 11, comprising: reducing porosity of said casting with said HIP process.
 14. The method of claim 12, comprising: improving corrosion resistance of said casting by said HIP process.
 15. The method of claim 13, comprising: increasing strength of said casting by said HIP process.
 16. The method of claim 14, comprising: producing engaging components of the downhole tool.
 17. The method of claim 15, comprising: producing a seat for a flapper in a safety valve.
 18. The method of claim 16, comprising: producing a flow tube for a safety valve. 